---
layout: "default"
title: "_SequenceWrapper"
description: "Swift documentation for '_SequenceWrapper': A type that is just a wrapper over some base Sequence."
keywords: "_SequenceWrapper,protocol,swift,documentation,Base,Iterator"
root: "/v3.0"
---

<div class="intro-declaration"><code class="language-swift">protocol _SequenceWrapper</code></div>

<div class="discussion comment">
    <p>A type that is just a wrapper over some base Sequence</p>
</div>

<table class="standard">
<tr>
<th id="inheritance">Inheritance</th>
<td>
<span class="viz"><a href="hierarchy/">View Protocol Hierarchy &rarr;</a></span>
</td>
</tr>

<tr>
<th id="aliases">Associated Types</th>
<td>
<span id="aliasesmark"></span>
<div class="declaration">
<code class="language-swift">Base : Sequence</code>
</div>
<div class="declaration">
<code class="language-swift">Iterator : IteratorProtocol = Self.Base.Iterator</code>
</div>
</td>
</tr>


<tr>
<th>Import</th>
<td><code class="language-swift">import Swift</code></td>
</tr>

</table>









<h3>Default Implementations</h3>





<h4>Where Self : Sequence, Iterator == Base.Iterator</h4>


<div class="declaration" id="self_-sequence-iterator-base-iterator-var-underestimatedcount_-int">
<a class="toggle-link" data-toggle="collapse" href="#comment-self_-sequence-iterator-base-iterator-var-underestimatedcount_-int">var underestimatedCount: Int</a><div class="comment collapse" id="comment-self_-sequence-iterator-base-iterator-var-underestimatedcount_-int"><div class="p">
    <p>Returns a value less than or equal to the number of elements in
the sequence, nondestructively.</p>

<p><strong>Complexity:</strong> O(<em>n</em>), where <em>n</em> is the length of the sequence if the
  sequence is a collection or wraps a collection; otherwise, O(1).</p>

    <h4>Declaration</h4>    
    <code class="language-swift">var underestimatedCount: Int { get }</code>

    </div></div>
</div>





